The #toolbar-menubar has three pixels of bottom and top margin located in chrome://ctraddon_os_special/skin/tabsontop_offextra.css that I absolutely can not figure out how to negate. Here is one of many examples of what I attempted using userChrome.css yet the selectors just aren't applying:

After considerable more research I discovered it's hard coded in the Classic Theme Restorer theme. I've unzipped all the assets and have had to manually weed out about a dozen bad styles that weren't necessary to begin with. I don't need any more updates for that extension any way. Thanks for trying guys.